Project Summary Autografts and allografts are current standard strategies for bone repair. However, each possesses limita- tions, such as donor-site morbidity with the use of autograft and the risk of disease transmission with the use of allograft. Synthetic bone-graft substitute based on a tissue engineering strategy has represented an alternative approach to overcome these inherent limitations. In 2009, close to 1.5 billion dollars were spent on bone-graft substitutes, half of which was attributed to recombinant human BMPs (rhBMPs). rhBMP-2 have been approved for inducing spinal fusion, fracture healing, and filling bony defects following tumor resection. In dentistry, rhBMP-2 also have been used in alveolar ridge and sinus augmentation. rhBMP-7 is also used as an autograft alternative for recalcitrant long bone nonunions. However, the outcome of rhBMPs is far from satisfactory. Thus, the high cost associated with rhBMPs therapy and the reported adverse events following its usage in supra physiological doses strongly underscore the need to develop an alternative approach that is safer, more cost-effective, and highly efficient for bone regeneration. Our long-term goal is to develop a microRNA (miR)- based gene therapy program that can be used to effectively promote osteogenic differentiation and bone re- generation. MiR-200c is a member of the miR-200 family that is involved in regulation of mesenchymal-to- epithelial transition and stem cell proliferation and differentiation. Recent studies demonstrated that miR-200c inhibits both Noggin and multiple proinflammatory factors, including NF-kB and IL-8. These factors have been demonstrate to reduce osteogenic differentiation and bone formation. In our pilot studies we have shown that the overexpression of miR-200c can significantly increase the expression of Runx2, a key transcription factor of osteoblasts, in human bone marrow mesenchymal stem cells (MSCs) and up-regulate multiple osteogenic biomarkers in human preosteoblasts. Our objective in this application is to establish a proof of concept in which miR-200c can be used to develop a novel, miR-based therapeutics for bone regeneration. The central hypothesis is that miR-200c delivered by a non-viral vector will significantly promote osteogenic differentiation and bone formation in vitro and in vivo. In this project, we will determine the molecular function of miR-200c delivered by polyethylenimine nanoparticles in osteogenic differentiation of human bone marrow MSCs (Aim 1) and the efficacy of this approach to induce bone regeneration in vivo (Aim 2). At the completion of this project, it is our expectation that we will significantly expand understanding of the molecular function and potential mechanisms mediated by miR-200c on osteogenic differentiation of human bone marrow MSCs. The in vivo study will establish a proof of concept in which miR-200c can be used to promote bone formation. We also will seek translational capabilities of this small molecule delivered by a non-viral system as an alternative approach for clinical application of bone regeneration.